Merge pull request #1171 from haukepetersen/example_ipcpingpong_readme

examples: added README.md to ipc_pingpong example

examples/ipc_pingpong/README.md

+IPC Pingpong!
+=============
+
+This example is to illustrate the usage of RIOTs IPC messaging system.
+
+The application starts a second thread (in addition to the main thread) and sends messages between
+these two threads. The main thread calls `thread_send_receive()` in an endless loop. The second
+thread receives the message, prints `2nd: got msg from x` to stdout and sends a reply message with
+an incrementing number back to the main thread. The main thread then prints the number it received
+from the 2nd thread.
+
+The correct output should look like this:
+```
+This is RIOT! (Version: xxx)
+kernel_init(): jumping into first task...
+Starting IPC Ping-pong example...
+1st thread started, pid: 1
+2nd thread started, pid: 2
+2nd: Got msg from 1
+1st: Got msg with content 2
+2nd: Got msg from 1
+1st: Got msg with content 3
+2nd: Got msg from 1
+1st: Got msg with content 4
+2nd: Got msg from 1
+1st: Got msg with content 5
+2nd: Got msg from 1
+1st: Got msg with content 6
+2nd: Got msg from 1
+1st: Got msg with content 7
+2nd: Got msg from 1
+1st: Got msg with content 8
+2nd: Got msg from 1
+1st: Got msg with content 9
+2nd: Got msg from 1
+1st: Got msg with content 10
+[...]
+```

examples/ipc_pingpong/main.c

 /*
- * Copyright (C) 2013 Freie Universität Berlin
+ * Copyright (C) 2014 Freie Universität Berlin
  *
  * This file is subject to the terms and conditions of the GNU Lesser General
  * Public License. See the file LICENSE in the top level directory for more
@@ -14,6 +14,7 @@
  * @brief       IPC pingpong application
  *
  * @author      Kaspar Schleiser <kaspar@schleiser.de>
+ * @author      Hauke Petersen <hauke.petersen@fu-berlin.de>
  *
  * @}
  */
@@ -26,12 +27,12 @@
 
 void second_thread(void)
 {
-    printf("second_thread starting.\n");
+    printf("2nd thread started, pid: %i\n", thread_getpid());
     msg_t m;
 
     while (1) {
         msg_receive(&m);
-        printf("2nd: got msg from %i\n", m.sender_pid);
+        printf("2nd: Got msg from %i\n", m.sender_pid);
         m.content.value++;
         msg_reply(&m, &m);
     }
@@ -41,7 +42,8 @@ char second_thread_stack[KERNEL_CONF_STACKSIZE_MAIN];
 
 int main(void)
 {
-    printf("Hello world!\n");
+    printf("Starting IPC Ping-pong example...\n");
+    printf("1st thread started, pid: %i\n", thread_getpid());
 
     msg_t m;
 
@@ -53,6 +55,6 @@ int main(void)
 
     while (1) {
         msg_send_receive(&m, &m, pid);
-        printf("Got msg with content %u\n", m.content.value);
+        printf("1st: Got msg with content %u\n", (unsigned int)m.content.value);
     }
 }